The present invention relates a method and an apparatus for manufacturing organic EL display devices that exhibit high precision and excellent visibility. The organic EL display devices can be applied to display devices in a wide variety of equipment, including portable terminals and industrial instruments.
In recent years, both the speed of information communication and expansion of application area have rapidly increased. In these circumstances, a wide variety of display devices have been proposed to meet the requirements of portability and animation display, while exhibiting low power consumption, high speed response, and high precision.
In color display systems, a type of color display device has been devised that employs a driving system using thin film transistors (TFTs). In this system, the type of devices in which light is emitted from the side of the substrate having the TFTs cannot attain high aperture due to the intercepting effect of wiring parts. Accordingly, a so-called top emission type has recently been employed in which light is emitted from the side of the substrate opposite to that on which the TFTs are formed.
The possibility of providing an organic EL display device with high precision and high luminosity are being demonstrated with a combination of the top emission system and a color conversion system in which multi-color fluorescent light is emitted from each of fluorescent bodies separately distributed and absorbing excited light. See, for example, Japanese Unexamined Patent Application Publication Nos. H11-251059 and 2000-77191.
FIG. 5 shows a schematic cross-sectional view of a structure of a prior art organic EL display. On substrate 602 are formed TFTs 604, bottom electrode 606, organic EL layer 608, and top electrode 610. On transparent substrate 616, color conversion filter layer 612 and black masks 614 are formed. Then, on the edges of the substrate 602, peripheral sealing layer 618 is formed using a two liquid type epoxy adhesive that cures at room temperature, for example. The peripheral sealing layer is bonded with transparent substrate 616. Internal space 620 is formed between the two substrates.
This structure has, however, a problem of degradation of light emission efficiency of the display device, because a part of the light emitted from organic EL layer 608 is reflected at the boundary between internal space 620 and top electrode 610 and/or at the boundary between internal space 620 and color conversion filter layer 612.
Japanese Unexamined Patent Application Publication No. H11-283739 proposes a way of suppressing reflection at the boundaries by filling the internal space with adhesive when the cover substrate is bonded to the organic EL light emitting device of top emission type. The cover substrate in this approach is intended only to seal an organic EL light emitting device. This document does not disclose provision of a color conversion filter layer on the cover substrate and does not mention alignment between a color conversion filter layer and an organic EL light emitting device.
Japanese Unexamined Patent Application Publication No. 2002-229042, on the other hand, discloses a process in which bonding and simultaneous alignment in a vacuum chamber is conducted in manufacturing process of liquid crystal display devices.
There is a need, therefore, to suppress reflection inside of the display device to improve light emitting efficiency in a display device made by bonding an organic EL light emitting device and a color conversion filter. In this context, it is important to avoid the generation of voids on the contact plane of the filler material with the organic EL light emitting device and/or with the color conversion filter, and to keep parallelism between the substrate of the organic EL light emitting device and the substrate of the color conversion filter by deformation of the filler material in the process of bonding during the process of filling the internal space with a filler material are. This is because reflection and refraction of light from the organic EL light emitting device occur at the voids, resulting in degradation of emission efficiency and display quality.
A method in which an opening for injecting filler material is provided in a bonding layer disposed in the periphery of either substrate, the two substrates are bonded, following which a filler material is injected through the opening and the opening is sealed off to provide an end seal would present additional problems. Such a method would require the additional steps of boring the opening in the bonding layer and end sealing, steps which would increase the cost.
Another possible method would be first to put a filler material on one of the substrates and then to pressure bond the organic EL light emitting device and the color conversion filter while aligning the two. However, air might enter during this process, causing bubble inclusion when the pressure bonding is conducted in the atmospheric pressure. Or alternatively, the pressure bonding would be conducted in a vacuum. Although the air causing bubble inclusion could be removed by conducting the pressure bonding in a vacuum, alignment in a vacuum requires complicated equipment and again raises production cost.
Therefore, a method is needed that fills the internal space between the organic EL light emitting device and the color conversion filter with a filler material without inclusion of bubbles, while at the same time facilitating alignment of the organic EL light emitting device and the color conversion filter.
Not only must air be prevented from entering the filler material, but also water inclusion should be avoided in the internal space between the organic EL light emitting device and the color conversion filter and in the filler material for filling the internal space. The water included in the internal space and/or the filler material diffuses into an organic light emitting layer of the organic EL light emitting device and generates spots incapable of light emission (so-called dark spots).
Therefore, a method is also needed that avoids this problem and prevents the water inclusion in the internal space and the filler material in the process of bonding the organic EL light emitting device and the color conversion filter.